In the current field of image display technology, TFT LCD (Thin Film Transistor Liquid Crystal Display) stands out owing to its excellent performances and rapidly expands in various application fields, such as mobile phones, computers, televisions, etc. In a liquid crystal display device, transmittance of the backlight is controlled by deflection of non-luminous liquid crystal molecules while under the effect of voltage, such that a function of image display is realized. In view of this, improvement of the operating performances of a backlight module has become an important developing trend in the display technology.
At present, for the mainstream manufacturers of liquid crystal display devices, a boost converter with a pulse width modulation dimming function, as shown in FIG. 1, is used as a drive circuit for the backlight like LED lamps to supply an operating voltage for the LED lamps and adjust the magnitude of the operating voltage in order to control the luminance of the LED lamps. In this circuit, a drive control unit is one of the key circuit units, and it plays a role of modulating a sawtooth-wave signal based on an input control signal to output a pulse width modulation dimming signal (referred to as PWM dimming signal for short) with a particular duty cycle. The PWM dimming signal is used for modulating a voltage signal Vin output to the LED lamps from a power supply, and a modulated voltage signal Vout is loaded onto the LED lamps to drive the LED lamps. Meanwhile, in order to achieve short response time and good voltage stabilizing effect, a voltage at the LED lamps is collected as a feedback voltage VFB, and is supplied to an error amplification unit located at the pre-stage of the drive control unit. The feedback voltage VFB is compared with a predetermined reference voltage VREF at an input terminal of the error amplification unit, and the comparison result is amplified by the error amplification unit to serve as a control signal for adjusting the duty cycle of the PWM dimming signal and then supplied to the drive control unit. By mean of this, the drive control unit is controlled to output a PWM dimming signal with an appropriate duty cycle, such that adjustment to the operating voltage Vout of the LED lamps is achieved.
Typically, the liquid crystal display device needs to be switched back and forth between different operating modes during displaying, and provides, e.g., a black pattern, a white pattern and gray scale patterns with various luminance. Thus, the LED lamps, which serve as a light source for the liquid crystal display device, also need to operate under different modes, e.g., a low loading mode when the black pattern is provided, a high loading mode when the white pattern is provided and an intermediate mode when those gray scale patterns are provided. The response rate (or response time) of above mode switching is one of the important indicators to evaluate the imaging performance of a display device.
In the prior art, in order to meet the requirements of all LED lamps in a backlight, such as luminance, error and voltage stabilization, the relevant parameters of a backlight drive circuit are typically designed in accordance with the most extreme situation, i.e., switching from the low loading mode to the high loading mode and from the high loading mode to the low loading mode, such that the backlight drive circuit and the display device thereof have relatively reasonable response rates. Such a “one-size-fits-all” design pattern, although simple and convenient, may lead to a low overall response rate due to failure of considering the intermediate modes having very small luminance scales but emerging mostly in practical use, such that the problems, such as INRUSH noise, instability of power supply system, etc. may be aroused. Accordingly, the present disclosure provides, on the basis of the prior art, a backlight drive circuit capable of adjusting response rate for different loading modes, and a liquid crystal display and a drive method using the same.